The present invention relates to a memory package system in which an operating power source is supplied from a read/write unit to a memory module in a contactless manner and a data transmission is executed between them and, more particularly, to a memory package system using a spread spectrum communication technique in the data transmission.
The inventors of the present invention have proposed a memory package system in U.S. patent application Ser. No 07/141,222 (1988), now U.S. Pat. No. 4,855,994, in which data is bidirectionally transmitted between a memory module having therein a nonvolatile memory and a read/write unit by the contactless electromagnetic coupling using induction coils, thereby writing or reading the data.
In the memory package system, frequencies f.sub.1 and f.sub.2 are switched in correspondence to the data bits 0 and 1 of a transmission signal and the frequency modulation is executed by a multiplexer provided in the read/write unit, and the modulation signal is transmitted to the memory module by a pair of induction coils for a down signal.
In the memory module, the reception signal received by the induction coil is rectified to produce a power source in the memory, the data bits 0 and 1 are demodulated from the reception signal, and data is written into the nonvolatile memory unit by the code based on a combination of the data bits 0 and 1 or the data is read out of the nonvolatile memory unit.
The data which was read out of the nonvolatile memory unit is not modulated for the data bit 0 but is modulated by a frequency f.sub.3 only for the data bit 1. The modulation signal is transmitted to the read/write unit through the pair of induction coils for an up signal. In the read/write unit, the reception signal of the induction coil is demodulated to thereby obtain the read data 0 and 1.
However, such a conventional frequency modulation system for modulating at the different frequency signals in accordance with the data bits 0 and 1 is based on electromagnetic inductive coupling by induction coils using coils and magnetic cores. Therefore, a transfer energy of the electromagnetic inductive coupling is generally attenuated in inverse proportion to the cube of the distance between the coils and a value within a range from about a few mm to ten and a few mm is a practical limit value.
On the other hand, the read/write unit for writing and reading data into/from the memory module is constructed by a digital circuit and a microprocessor. However, the spike-like noises which are generated by the digital circuit and microprocessor have energy in an extremely wide band. The noises generated from them interfere with the reception signal and deteriorate the S/N ratio of the memory module.
On the other hand, in the memory module, the reception signal from the read/write unit is rectified to form an internal power source, so that a driving electric power for data communication needs to be minimized. Particularly, it is necessary to reduce the transmission energy.